Two bit optical analog-to-digital converter based on photonic crystals

In this paper, we demonstrate a 2-bit optical analog-to-digital (A/D) converter. This converter consists of three cascaded splitters constructed in a self-guiding photonic crystal through the perturbation of the uniform lattice. The A/D conversion is achieved by adjusting splitting ratios of the splitters through changing the degree of perturbation. In this way, output ports reach a state of '1' at different input power levels to generate unique states desired for an A/D converter. To validate this design concept, we first experimentally characterize the relation between the splitting ratio and the degree of lattice perturbation. Based on this understanding, we then fabricate the 2-bit A/D converter and successfully observe four unique states corresponding to different power levels of input analog signal.